This invention relates to a method of controlling the welding in a three-dimensional X-Y-Z coordinate system.
Especially in shipbuilding robotized welding of shaped pieces has not been possible in practical production on one hand due to programming problems and on the other hand due to the accuracy of manufacture. In practice, the dimensional accuracy of the piece and its positioning accuracy have not reached a sufficiently high level that the robotizing could be based for instance on information obtained from the design system. Efforts have been made to solve the problems by specifying the manufacture of components and the positioning accuracy and by developing programming systems based e.g. on simulation. Then, however, serious problems have been encountered both in the technical realization and in expense.
U.S. patent application Ser. No. 09/941,485 (now U.S. Pat. No. 6,750,426) discloses a method of flat welding pieces by utilizing a welding robot and an artificial vision system. Thus, the structure to be welded, which is arranged on a support surface, is first photographed and then on the basis of the produced picture map the points to be welded are identified and the corresponding welding parameters are determined, and the welding parameters are passed to the welding machine so as to control the welding. Programmable macro programs may be utilized in the welding. This method is advantageous in itself, but it is not as such applicable to the welding of three-dimensional curved pieces.
U.S. Pat. No. 5,999,642 discloses a method and an arrangement for photographing a three-dimensional structure for welding. The structure is photographed by scanning it with a sufficient number of cameras and/or from several angles so as to fully define the structure to be welded and subsequently the structural information is passed to a welding program, which controls a welding robot. Complete visual information on the whole three-dimensional structure is produced and by means of that information the operation of the welding robot is controlled in the real world. A mathematical model of the structure to be welded is produced. The method is laborious and its image processing is complicated, and therefore the method is quite time-consuming. Inaccuracies related to the practical welding process cannot be avoided by using this method.